Pneumatic conveyance of particles is used in a wide range of processes worldwide. One process that uses pneumatic conveyance of particles is associated with abrasive fluid jet systems, which may be used in production cutting applications. Abrasive fluid jets are used to cut, drill holes through, or machine relatively hard materials such as glass, stone, and metals. Abrasive fluid jet cutting generally operates using a high speed jet of fluid to project abrasive particles to erode a workpiece. The high speed fluid jet is generated by using a high pressure pump to deliver high pressure fluid to a nozzle, where the high pressure is converted to a high velocity fluid jet. The vacuum of the jet is used to convey abrasive particles such as garnet to the cutting head where they are accelerated by the fluid jet in a mixing tube just downstream from the water orifice.
Abrasive fluid jet systems typically depend on an uninterrupted flow of abrasive particles from an abrasive supply system. If the flow of the abrasive particles is interrupted, cutting failure typically results. Cutting failures may be a reduction of cutting edge quality possibly resulting in failure to separate the workpiece. This may result in loss of a machined part, waste of material, loss of machine time, or other potentially costly and time wasting effects. Therefore, it is desirable to provide a reliable abrasive flow monitoring system.
Unfortunately, many flow sensors suffer from erosion and/or other degradation effects when used to measure a flow including entrained abrasive particles. Other flow sensors are too expensive. Sensors based on measuring an absolute pressure or vacuum in an abrasive delivery system has proven to be susceptible to inaccuracies related to atmospheric pressure changes and/or other factors. Conventional sensing systems associated with pneumatic conveying systems have often failed to meet or only poorly meet needs for stability, durability, accuracy, reliability, and cost. What is needed is a reliable and cost effective method to reliably monitor the abrasive flow that does not suffer from rapid deterioration in a streaming abrasive environment.